Dynamic spinal stabilization assembly with elastic bumpers and locking limited travel closure mechanisms

ABSTRACT

A dynamic stabilization assembly includes a core, typically in the form of a tensioned cord, at least one pair of bone anchors, a spacer surrounding the core located between the bone anchors, at least one elastic bumper and at least one fixing or blocking member. The core is slidable with respect to at least one of the bone anchors, the spacer and the bumper. The bumper is compressed. Bone screws of the assembly include closure structures that lock against the bone screw independent of any fixing or sliding of the core with respect to the bone screw.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a division of U.S. Nonprovisional application Ser.No. 15/389,296 entitled, “DYNAMIC SPINAL STABILIZATION ASSEMBLY WITHELASTIC BUMPERS AND LOCKING LIMITED TRAVEL CLOSURE MECHANISMS,” filedDec. 22, 2016, which is a continuation of U.S. Nonprovisionalapplication Ser. No. 12/661,042 entitled “DYNAMIC SPINAL STABILIZATIONASSEMBLY WITH ELASTIC BUMPERS AND LOCKING LIMITED TRAVEL CLOSUREMECHANISMS,” filed Mar. 10, 2010, which claims priority under 35 U.S.C §119 from U.S. Provisional Application No. 61/210,058 entitled “DYNAMICSPINAL STABILIZATION ASSEMBLY WITH ELASTIC BUMPER AND LIMITED TRAVELCLOSURE,” filed Mar. 13, 2009. U.S. Nonprovisional application Ser. No.12/661,042 is also a Continuation-in-Part of U.S. patent applicationSer. No. 12/584,980 entitled “FLEXIBLE SPINAL STABILIZATION ASSEMBLYWITH SPACER HAVING OFF-AXIS CORE MEMBER,” filed Sep. 15, 2009, whichclaims the benefit of U.S. Provisional Application No. 61/192,312entitled “DYNAMIC SPINAL STABILIZATION ASSEMBLY WITH SPACERS ANDOFF-AXIS CORE,” filed Sep. 17, 2008. U.S. Nonprovisional applicationSer. No. 12/661,042 is also a Continuation-in-Part of U.S. patentapplication Ser. No. 12/148,465 entitled “DYNAMIC FIXATION ASSEMBLIESWITH PRE-TENSIONED CORD SEGMENTS,” filed Apr. 18, 2008, which claims thebenefit of U.S. Provisional Application No. 60/927,111 entitled “DYNAMICFIXATION ASSEMBLIES WITH PRE-TENSIONED CORD SEGMENTS,” filed May 1,2007. U.S. Nonprovisional application Ser. No. 12/661,042 is also aContinuation-in-Part of U.S. patent application Ser. No. 12/229,207entitled “POLYAXIAL BONE ANCHOR ASSEMBLY WITH ONE-PIECE CLOSURE,PRESSURE INSERT AND PLASTIC ELONGATE MEMBER,” filed Aug. 20, 2008, nowU.S. Pat. No. 8,353,932 issued Jan. 15, 2013, which claims the benefitof U.S. Provisional Application No. 60/994,083 entitled “POLYAXIAL BONEANCHOR ASSEMBLY WITH ONE-PIECE CLOSURE, PRESSURE INSERT AND PLASTICELONGATE MEMBER,” filed Sep. 17, 2007, and which is aContinuation-in-Part of U.S. patent application Ser. No. 11/894,001entitled “DYNAMIC STABILIZATION CONNECTING MEMBER WITH ELASTIC CORE ANDOUTER SLEEVE,” filed Aug. 17, 2007, now U.S. Pat. No. 8,292,926 issuedOct. 23, 2012, which claims the benefit of U.S. Provisional ApplicationNo. 60/851,353 entitled “DYNAMIC STABILIZATION CONNECTING MEMBER WITHELASTIC CORE AND OUTER SLEEVE,” filed Oct. 12, 2006. U.S. Nonprovisionalapplication Ser. No. 12/661,042 is also a Continuation-in-Part of U.S.patent application Ser. No. 11/328,481 entitled “DYNAMIC STABILIZATIONASSEMBLIES, TOOL SET AND METHOD,” filed Jan. 9, 2006, now U.S. Pat. No.7,862,587 issued Jan. 4, 2011, which claims the benefit of U.S.Provisional Application No. 60/736,112 entitled “DYNAMIC FIXATIONASSEMBLY WITH COIL AND THREADED CORE,” filed Nov. 10, 2005, U.S.Provisional Application No. 60/728,912 entitled “DYNAMIC FIXATIONASSEMBLY WITH COIL AND ADJUSTABLE SECTIONS,” filed Oct. 21, 2005, U.S.Provisional Application No. 60/725,445 entitled “DYNAMIC FIXATIONASSEMBLY WITH CYLINDRICAL CORE AND OUTER COIL-LIKE MEMBER,” filed Oct.11, 2005, and U.S. Provisional Application No. 60/722,300 entitled“DYNAMIC STABILIZATION MEDICAL IMPLANT ASSEMBLIES AND METHODS,” filedSep. 30, 2005. All of the above are fully incorporated by referenceherein for all purposes.

The present invention relates to apparatuses and methods for use inperforming spinal surgery and, in particular, to bone attachmentstructures for dynamic spinal support and alignment, preferably usingminimally or less invasive techniques.

Historically, it has been common to fuse adjacent vertebrae that areplaced in fixed relation by the installation there along of bone screwsor other bone anchors and cooperating longitudinal connecting members orother elongate members. Fusion results in the permanent immobilizationof one or more of the intervertebral joints. Because the anchoring ofbone screws, hooks and other types of anchors directly to a vertebra canresult in significant forces being placed on the vertebra, and suchforces may ultimately result in the loosening of the bone screw or otheranchor from the vertebra, fusion allows for the growth and developmentof a bone counterpart to the longitudinal connecting member that canmaintain the spine in the desired position even if the implantsultimately fail or are removed. Because fusion has been a desiredcomponent of spinal stabilization procedures, longitudinal connectingmembers have been designed that are of a material, size and shape tolargely resist flexion, extension, torsion, distraction and compression,and thus substantially immobilize the portion of the spine that is to befused. Thus, longitudinal connecting members are typically uniform alongan entire length thereof, and usually made from a single or integralpiece of material having a uniform diameter or width of a size toprovide substantially rigid support in all planes.

An alternative to fusion, which immobilizes at least a portion of thespine, and the use of more rigid longitudinal connecting members orother rigid structure has been a “soft” or “dynamic” stabilizationapproach in which a flexible loop-, S-, C- or U-shaped member or acoil-like and/or a spring-like member is utilized as an elasticlongitudinal connecting member fixed between a pair of pedicle screws inan attempt to create, as much as possible, a normal loading patternbetween the vertebrae in flexion, extension, distraction, compression,side bending and torsion. Another type of soft or dynamic system knownin, the art includes bone anchors connected by cords or strands. Such acord or strand may be threaded through cannulated spacers that aredisposed between adjacent bone anchors when such a cord or strand isimplanted, tensioned and attached to the bone anchors. The spacerstypically span the distance between bone anchors, providing limits onthe bending movement of the cord or strand and thus strengthening andsupporting the overall system. The cords or strands utilized in suchsystems typically are stretched or pulled to maximum tension, followedby fixing the cords to adjoining bone screws. A variety of specializedtools for holding and stretching the cords are required for such anoperation. Although easily bendable, the cords or strands utilized insuch systems do not allow for elastic distraction of the system onceimplanted because the cord or strand must be stretched or pulled tomaximum tension in order to provide a stable, supportive system.

SUMMARY OF THE INVENTION

A dynamic stabilization assembly according to the invention forattachment to at least two bone anchors includes an elongate inner core,preferably a tensioned cord, with at least one spacer, typically in theform of an elastic spacer, surrounding the core, the core and spacerdisposed between the at least two bone anchors. An elastic bumper and afixing structure or blocker are disposed on an opposite side of one ofthe bone anchors, the bumper in compression by cooperation between oneof the bone anchors and the blocker.

In a method of one aspect of the invention, a cord and surroundingspacer are inserted between first and second implanted bone anchors withthe spacer being in contact with both of the bone anchors. The cord isfixed to the first bone anchor. A bumper and a fixing structure orblocker are threaded along the cord until the bumper abuts the secondbone anchor and the blocker abuts the bumper. The cord is tensioned andthe blocker is crimped or otherwise fixed to the cord, such as by a setscrew, resulting in a tensioned cord with both the bumper and the spacerbeing in compression. The cord remains in sliding engagement with thesecond bone anchor, advantageously allowing for some elastic distractionof the system with elongation between the screw heads once implanted, aswell as compression and bending in response to spinal flexion andextension. In other embodiments according the invention, the core cordmember may be replaced by relatively hard stiff rods or bars orrelatively soft, deformable or non-elastic rods or bars, or otherlongitudinal connecting members of different shapes and materials,including PEEK and other polymers and metal cables. Assemblies of theinvention may include mono- and polyaxial open and closed screws thatmay be used with a first locking fastener or closure top that fixesagainst the core member (cord, cable, rod or bar), or alternatively witha second locking limited travel closure top that is fixed to the bonescrew and captures the core (cord, cable, rod or bar) in the screw, butallows such core member to be in sliding engagement with the bone screw.In the case of a polyaxial screw, the polyaxial mechanism is configuredto be locked by this second closure top while allowing the core totravel through the screw head.

OBJECTS AND ADVANTAGES OF THE INVENTION

Objects and advantages of the invention include providing lightweight,reduced volume, low profile stabilization assemblies, including at leasttwo bone anchors and a longitudinal connecting member therebetween thatcomprises a core and spacer and an end bumper-blocker combination.Furthermore, it is an object of the invention to provide apparatus andmethods that are easy to use and especially adapted for the intended usethereof and wherein the apparatus are comparatively inexpensive to makeand suitable for use.

Other objects and advantages of this invention will become apparent fromthe following description taken in conjunction with the accompanyingdrawings wherein are set forth, by way of illustration and example,certain embodiments of this invention.

The drawings constitute a part of this specification and includeexemplary embodiments of the present invention and illustrate variousobjects and features thereof.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an enlarged and partial perspective view of a dynamicstabilization connector of the invention having an inner cord, an outerspacer, an elastic bumper and a fixing structure or blocker, shown as acrimping structure, the connector shown with a pair of open monoaxialbone screws, one with a cord travel or sliding closure top and one witha cord compressing and locking closure top.

FIG. 2 is a partial and reduced and exploded front elevational view ofthe connector and bone screws of FIG. 1 , shown without the closuretops.

FIG. 3 is a partial front elevational view, similar to FIG. 2 showing astage of assembly of the connector and bone screws of FIG. 1 , showinguse of a driving tool for fixing one of the first closure tops againstthe cord.

FIG. 4 is a partial top plan view with portions broken away to show thedetail thereof, showing use of a crimping tool in a further stage ofassembly of the connector and bone screws of FIG. 1 .

FIG. 5 is an enlarged and partial cross-sectional view taken along theline 5-5 of FIG. 1 .

FIG. 6 is an exploded perspective view of an alternative bone screw foruse with the invention of FIG. 1 , shown with a cord and a cord slidinglimited travel closure top.

FIG. 7 is a partial perspective view of an alternative bar for use withthe bone screw and closure top of FIG. 6 .

FIG. 8 is an enlarged and partial cross-sectional view of the bone screwof FIG. 6 taken along the line 8-8 of FIG. 6 and showing a portion ofthe cord in phantom.

FIG. 9 is an enlarged and partial cross-sectional view taken along theline 9-9 of FIG. 8 and also showing the mated closure top in crosssection and a portion of the cord in phantom.

FIG. 10 is an exploded perspective view of the bone screw of FIG. 6shown with a second locking closure top and a deformable rod.

FIG. 11 is a partial cross-sectional view taken along the line 11-11 ofFIG. 10 and showing the second locking closure top in an early stage ofassembly.

FIG. 12 is a partial cross-sectional view, similar to FIG. 11 , showingthe second closure top fully assembled within the bone screw and engagedwith and compressing a deformable rod.

FIG. 13 is an enlarged and partial cross-sectional view of the bonescrew of FIG. 10 taken along the line 11-11, with a portion of thedeformable rod being shown in phantom.

FIG. 14 is an enlarged and partial cross-sectional view, taken along theline 14-14 of FIG. 13 , also showing the mated closure top and a portionof the deformable rod in cross-section.

FIG. 15 is a perspective view of another alternative embodiment of adynamic stabilization connector of the invention having an inner rod, anelastic bumper and a blocking structure, the connector shown with a pairof open polyaxial bone screws.

FIG. 16 is an enlarged and partial side elevational view of one of thebone screws of the embodiment of FIG. 15 with portions broken away toshow the detail thereof.

DETAILED DESCRIPTION OF THE INVENTION

As required, detailed embodiments of the present invention are disclosedherein; however, it is to be understood that the disclosed embodimentsare merely exemplary of the invention, which may be embodied in variousforms. Therefore, specific structural and functional details disclosedherein are not to be interpreted as limiting, but merely as a basis forthe claims and as a representative basis for teaching one skilled in theart to variously employ the present invention in virtually anyappropriately detailed structure. It is also noted that any reference tothe words top, bottom, up and down, and the like, in this applicationrefers to the alignment shown in the various drawings, as well as thenormal connotations applied to such devices, and is not intended torestrict positioning of the connecting member assemblies of theapplication and cooperating bone anchors in actual use.

With reference to FIGS. 1-5 , the reference numeral 1 generallydesignates a non-fusion longitudinal dynamic stabilization connectorassembly of the invention. The illustrated assembly 1 includes thefollowing components: an elongate bendable and flexible core in the formof a cord 4; at least one cannulated spacer 6; an elastic bumper 8; anda fixing structure or blocking member, such as a crimping structure 10.The assembly 1 is shown with a pair of open monoaxial bone screws,generally 12, the assembly 1 extending substantially linearly along acentral axis A in FIG. 3 , for example. For purposes of thisapplication, the identical bone screws 12 are identified as 12A and 12Bas the one bone screw 12A cooperates with a first locking and cordpressing closure top 14 and the other bone screw 12B cooperates with asecond locking limited travel closure top 15 that allows for slip orslide of the cord 4 within the bone screw 12B. The closure tops 14 and15 are substantially similar to one another with the exception that thetop 15 is sized and shaped to bottom out on a lower seating surface 17of a run-out of an inner guide and advancement structure 18 of the bonescrew 12 that mates with the outer guide and advancement structure ofthe closure top 14 or the closure top 15. The closure top 14 furtherincludes an end or bottom portion 19 that extends beyond the run-outseating surface 17 and abuts against and fixes the cord to the bonescrew. The guide and advancement run-out seating surface 17 is bestshown and described with respect to an alternative bone screw 112 and112′ described in greater detail below with reference to FIGS. 6-14 .Also, as will be described in more detail below, the bone screw 12Acooperates with the closure top 14 to fix a portion of the cord 4 to thebone screw 12A while the bone screw 12B engages and fixes the closuretop 15 to the screw 12B to capture a portion of the cord 4 within thebone screw 12B, but allow for sliding movement of the cord 4 withrespect to the bone screw 12B. The elongate inner cord core 4 isslidingly received within the spacer 6 and the bumper 8, and initiallywithin the blocker or crimping structure 10, as will be described ingreater detail below. The cord 4 is eventually tensioned and fixed insuch tensioned state by the crimping structure 10 and the bone screw12A. In other embodiments according to the invention, the structure 10may include a threaded aperture (not shown) and further include acooperating set screw in addition to or in lieu of crimping. In suchembodiments, the set screw rotatably mates with the structure 10 at thethreaded aperture and is rotated until a bottom surface of the screwpresses against and, in some embodiments, penetrates the cord, fixingthe cord within the structure 10. As will be described in greater detailbelow, when fully assembled and all the components are fixed in positionas shown in FIGS. 1 and 5 , for example, the cord 4 is in tension, thespacer 6 may be in compression or in a neutral state, and the bumper 8is in compression.

It is noted that in other embodiments according to the invention, boththe bone screws 12A and 12B may be mated with a locking limited travelclosure top 15 and at least one additional blocker or crimping structureis included generally opposite the crimping structure 10 in the overallassembly to result in a cord that is tensioned along the assembly but insliding cooperation with two or more bone anchors of such assembly. Itis also noted that additional spacers 6 and bone screws 12 cooperatingwith closure tops 15 may be utilized according to the invention,providing longer assemblies of the invention with one of the spacers 6placed between each bone screw and the bumper 8 and the crimpingstructure 10 placed at one or both ends of such assembly next to a bonescrew 12 cooperating with a closure top 15 or two such closure tops 15.Also, as described in greater detail below, bone screws, spacers,bumpers and crimping structures or other blockers of the invention maybe sized, shaped and used with hard or deformable rods and bars,alternatively to the cord 4.

Although the screws 12 are illustrated, it is noted that the assembly 1may cooperate with a variety of bone screws and other bone anchors,including closed bone screws, hinged bone screws, polyaxial bone screws,with or without compression inserts, and bone hooks that may in turncooperate with a variety of closure structures having threads, flanges,or other structure for fixing the closure structure to the bone anchor,and may include other features, for example, external or internaldrives, break-off tops and inner set screws. A closed bone anchor withor without a set screw may also be used in the invention to capture thecord 4 in sliding, but not fixed engagement. The bone anchors, closurestructures and the connecting member 1 are then operably incorporated inan overall spinal implant system for correcting degenerative conditions,deformities, injuries, or defects to the spinal column of a patient.

The connecting member assembly 1 is elongate, with the inner core 4being any flexible elongate material including, but not limited tocords, threads, strings, bands, cables or fibers that may be single ormultiple strands, including twisted, braided or plaited materials. Theillustrated cord 4 has a substantially uniform body 20 of substantiallycircular cross-section, a first end 22 and an opposed second end 24, thecord 4 being cut to length as required by the surgeon. Initially, thecord 4 is typically of a length longer than shown in the drawings toallow for gripping of the cord 4 during assembly with the othercomponents of the assembly 1 and also for tensioning and attachment tothe bone screws 12A and 12B as will be described in greater detailbelow. The cord 4 may be made from a variety of materials, includingpolyester or other plastic fibers, strands or threads, such aspolyethylene-terephthalate. The cord 4 may be placed under axial tensionprior to final installation between the bone screws 12A and 12B, forexample by being tensioned along the axis A for a selected time tolengthen and otherwise deform the cord 4 during a primary creep stage.After the cord 4 reaches a secondary or steady-state creep, furthertension is placed on the cord 4 in preparation for fixing between thebone screw 12A and the crimping structure 10 as will be described ingreater detail below. It is noted that the cord 4 typically does notillustrate elastic properties, such as any significant additionallengthening with axial traction, after the assembly 1 is operativelyassembled within a human body, but the elastic bumper 8 will allow forrelative movement between the fully stretched cord 4 and the bone screw12B in response to spinal flexion, extension and any movement that maydraw the bone screw 12B away from the bone screw 12A.

With particular reference to FIGS. 1, 2 and 5 , the spacer 6 is sizedand shaped to be slidingly received over the cord 4 and may be made froma variety of elastic and more rigid materials, including, but notlimited to natural or synthetic elastomers such as polyisoprene (naturalrubber), and synthetic polymers, copolymers, and thermoplasticelastomers, for example, polyurethane elastomers such aspolycarbonate-urethane elastomers. In order to have low or no weardebris, the spacer 6 inner and side surfaces may be coated with anultra-thin, ultra hard, ultra slick and ultra-smooth coating, such asmay be obtained from ion bonding techniques and/or other gas or chemicaltreatments. The illustrated spacer 6 has an external substantiallycylindrical outer surface 28 and an internal substantially cylindricalsurface 30. The surface 30 is sized and shaped to closely cooperate andfit about the cord 4 and yet allow some sliding movement of the cord 4with respect to the spacer 6 along the axis A. The spacer 6 includesopposed substantially planar and annular end surfaces 32 and 34 that aresized and shaped to abut against planar surfaces of the bone screws 12Aand 12B, respectively. When initially assembled with the othercomponents of the connecting member assembly 1, the surfaces 32 and 34are substantially perpendicular to the axis A. It is foreseen that insome embodiments, the spacer 6 may be of smaller or larger outercircular cross section, or of a square, rectangular or other inner orouter cross-section including other curved or polygonal shapes. Thespacer 6 may further include one or more compression grooves that allowfor some additional compression of the spacer 6 when pressed upon in anaxial direction between the bone anchors 12A and 12B. Typically, such acompression groove is substantially uniform and circular incross-section, being formed in the external surface 28 and extendingradially toward the internal surface 30. The spacer can have anoff-axial lumen.

Also with particular reference to FIGS. 1, 2 and 5 , the elastic bumper8 is annular and includes an outer cylindrical surface 40, an innercylindrical surface 42, an end surface 44 and an opposed end surface 46.The illustrated bumper 8 further includes a compression groove 48 thatallows for some additional compression of the bumper 8 when pressed uponin an axial direction A between the bone anchor 12B and the crimpingring 10. The compression groove 48 is substantially uniform and circularin cross-section, being formed in the external surface 40 and extendingradially toward the internal surface 42. Bumpers of the invention mayinclude one, none or a plurality of compression grooves. The innercylindrical surface 42 forms a bore sized and shaped for closelyreceiving the cord 4 therethrough as shown, for example, in FIG. 5 . Theend surfaces 44 and 46 are substantially parallel to one another, butcan also be non-parallel.

The bumper 8 may be made from a variety of elastic materials, including,but not limited to natural or synthetic elastomers such as polyisoprene(natural rubber), and synthetic polymers, copolymers, and thermoplasticelastomers, for example, polyurethane elastomers such aspolycarbonate-urethane elastomers. The bumper 8 is typically shorter inlength and more elastic than the spacer 6, but may be equal to or longerthan the spacer and of the same, greater or lesser durometer than thespacer 6. In order to have low or no wear debris, the bumper 8 inner andside surfaces may also be coated with an ultra-thin, ultra hard, ultraslick and ultra-smooth coating, such as may be obtained from ion bondingtechniques and/or other gas or chemical treatments.

The fixing structure or blocker, illustrated as the crimping structureor ring 10 is substantially cylindrical and includes an outer surface 50and an inner surface 52 forming a substantially cylindrical through borethat opens at planar end surfaces 54 and 56 and operatively extendsalong the axis A. The crimping ring 10 is sized and shaped to receivethe elongate cord 4 through the inner surface 52. The crimping ring 10further includes a pair of opposed crimp or compression grooves 58 thatare pressable and deformable inwardly toward the axis A upon tensioningof the cord 4 and pre-compression of the bumper 8 during assembly of theassembly 1. The crimping ring 10 is preferably made from a stiff, butdeformable material, including metals and metal alloys. It is foreseenthat in lieu of or addition to the crimping surface, the blocker couldinclude a threaded aperture and a mating locking set screw for engagingand pressing into the cord 4.

The bone screws generally 12, and in particular the illustrated screws12A and 12B are open, fixed, monoaxial screws, each having an upper cordreceiving portion 62 integral with a threaded bone attachment portion orshank 64. The portion 62 further includes a substantially U-shapedchannel 66 for closely receiving the cord 4 therethrough, the channel 66further having an upper closure top receiving portion with the helicallywound guide and advancement structure 18 thereon for receiving andmating with the closure top 14 or the closure top 15. The upper,receiving portion 62 further includes opposed, substantially parallelside surfaces 70 that abut against side surfaces of the spacer 6 or thebumper 8. However, it is foreseen that according to the invention, otherembodiments of the invention may include side surfaces 70 that angleaway or towards one another for lordosing or kyphosing controllingembodiments as previously described in applicant's application U.S. Ser.No. 11/328,481, incorporated by reference herein.

To provide a biologically active interface with the bone, the threadedshanks 64 of the bone screws 12A and 12B may be coated, perforated, madeporous or otherwise treated. The treatment may include, but is notlimited to a plasma spray coating or other type of coating of a metalor, for example, a calcium phosphate; or a roughening, perforation orindentation in the shank surface, such as by sputtering, sand blastingor acid etching, that allows for bony ingrowth or ongrowth. Certainmetal coatings act as a scaffold for bone ingrowth. Bio-ceramic calciumphosphate coatings include, but are not limited to: alpha-tri-calciumphosphate and beta-tri-calcium phosphate (Ca3(PO₄)₂, tetra-calciumphosphate (Ca₄P₂O₉), amorphous calcium phosphate and hydroxyapatite(C₁₀(PO₄)₆(OH)₂). Coating with hydroxyapatite, for example, is desirableas hydroxyapatite is chemically similar to bone with respect to mineralcontent and has been identified as being bioactive and thus not onlysupportive of bone ingrowth, but actively taking part in bone bonding.

With particular reference to FIGS. 1, 2 and 5 , the closure structures14 and 15 can be any of a variety of different types of closurestructures for use in conjunction with the present invention withsuitable mating structure on the interior surface of the receiver 62 ofthe open bone screws 12. The illustrated closure structures 14 and 15are each rotatable between the spaced arms forming the receiver 62 andare substantially cylindrical, including an outer helically wound guideand advancement structure in the form of a flange form that operablyjoins with the guide and advancement structure 18. A driving tool 72illustrated in FIG. 3 is sized and shaped for engagement with aninternal drive feature 74 and is used for both rotatable engagement and,if needed, disengagement of the closure 14 and/or closure 15 from one ofthe receivers 62. The internal drive feature 74 may take a variety offorms and may include, but is not limited to, a hex shape (as shown),TORX or other features or apertures, such as slotted, tri-wing, spanner,two or more apertures of various shapes, and the like. As stated above,the closure 14 and the closure 15 are substantially identical with theexception of a height or depth dimension in the form of the portion orknob 19 that extends operatively perpendicular to the axis A. Theclosure structure 14 that includes the portion 19 is sized and shaped tobe long enough to compress against the cord 4 and frictionally fix thecord 4 in the receiver 62 when fully seated and mated with the guide andadvancement structure 18. (See, e.g., FIG. 14 that shows a similarclosure 114 that abuts against a run-out seat 117′ and has an extendedportion 119 for pressing down on a core, such as a cord or rod or bar).The illustrated closure top 14 may further include points or projectionsfor piercing into the cord 4 to provide enhanced contact and fixing ofthe cord 4 to the receiver 62. The closure 15 is sized and shaped to belong enough to fully seat within the receiver 62 and mate with the guideand advancement structure 18 run-out seating surface 17 in order to fixthe closure 15 in the bone screw and capture the cord 4 within thereceiver 62. However, the closure 15 is too short to fix the cord 4against the receiver 62. Rather, when the closure 15 is fully seated andmated in the receiver 62, the cord 4 remains in slidable relationshipwith the bone screw 12B and is not fixed against a surface of thereceiver 62. (See, e.g., FIG. 9 that shows a similar closure 115 thatabuts against a run-out seat 117 and is spaced from or in slidingengagement with a core, such as a cord or cable or rod or bar).

In use, the two bone screws 10 and 12 are implanted into vertebrae foruse with the dynamic connecting member 1. Each vertebra may bepre-drilled to minimize stressing the bone. Furthermore, if a cannulatedbone screw shank and/or closure top is utilized (as illustrated), eachvertebra will have a guide wire or pin (not shown) inserted therein thatis shaped for the bone screw cannula of the bone screw shank 64 andprovides a guide for the placement and angle of the shank 64 withrespect to the cooperating vertebra. A further tap hole may be made andthe shank 64 is then driven into the vertebra by rotation of a drivingtool (not shown) that engages a driving feature on or near the topportion 62 of the screw 12. It is foreseen that the screws 12A and 12Band the dynamic connector 1 can be inserted in a percutaneous orminimally invasive surgical manner.

With particular reference to FIGS. 2-4 , the dynamic connector assembly1 is assembled by inserting the cord 4 into the through bore formed bythe internal surface 30 of the spacer 6. Also as indicated in FIGS. 2and 3 , the cord 4 is first received into the U-shaped opening 66 of theopen bone screw 12A and the U-shaped opening 66 of the bone screw 12B,with the spacer 6 being disposed between facing surfaces 70 of bonescrews 12A and 12B. The closure top 14 is rotated and driven into thereceiver 62 of the bone screw 12A until the closure top 14 frictionallyengages the cord 4 and fixes the cord 4 to the screw 12A. Before orafter the closure top 14 is tightened, the closure top 15 may beinserted and rotated into the receiver 62 of the bone screw 12B untilthe top 15 is fully seated and engaged with such receiver run-outsurface 17, capturing but not fixing the cord 4 to the bone screw 12B.The bumper 8 is threaded along the cord 4 with the cord sliding throughthe through-bore formed by the inner surface 42 until the bumper face 44abuts against the surface 70 of the bone screw 12B located opposite thespacer 6. The crimping structure 10 is threaded along the cord 4 withthe cord sliding through the through-bore formed by the inner surface 52until the crimper face 54 abuts against the bumper face 46.

The cord 4 is tensioned and the bumper 8 is compressed against the bonescrew 12B by axial movement of the crimping structure 10 against thebumper 8, squeezing the bumper 8 between the bone screw 12B and thecrimping structure 10. The spacer 6 also may be compressed at this time.With particular reference to FIG. 4 , a crimping tool 80 is used tofrictionally attach the tensioned cord 4 to the crimping structure 10,thereby holding the cord 4 in tension between the bone screw 12A and thecrimping structure 10 and also compressing the bumper 8 against the bonescrew 12B.

The resulting connecting member assembly 1 is loaded with the cord 4 intension and the bumper 8 and optionally the spacer 6 in compression. Theassembly 1 is thus substantially dynamically loaded and orientedrelative to the cooperating vertebra, providing relief (e.g., shockabsorption) and protected movement in response to spinal flexion andextension, and further responding to distractive or tensioning forces aswell as to compressive forces.

If removal of the dynamic connector assembly 1 from the bone screws 12Aand/or 12B is necessary, or if it is desired to release the assembly 1at a particular location, disassembly is accomplished by using thedriving tool 72 with a driving formation cooperating with the closuretops 14 and 15 to rotate and remove the closure top from the bone screw12A and/or 12B. Disassembly is then accomplished in reverse order to theprocedure described previously herein for assembly.

With reference to FIGS. 6-9 , a bone screw 112 is illustrated that isidentical to the bone screw 12 of the assembly 1 with the exception thatthe U-shaped channel 66 formed by inner surfaces of the screw 12 hasbeen replaced with a substantially rectangular channel 166 formed byopposed planar surfaces 167 and a bottom planar surface 168. The bonescrew 112 has a receiver 162 and a shank 164, the receiver 162 having adiscontinuous guide and advancement structure 118 that is formed in theopposed surfaces 167. The bone screw 112 may be utilized in an assembly101 substantially similar to the assembly 1 that includes a cord 104identical or substantially similar to the cord 4 and further includesthe spacer 6, elastic bumper 8, crimping structure 10 of the assembly 1previously described herein. Because of the squared off shape of thechannel 166, the bone screw 112 may also be readily used with otherlongitudinal connecting members, such as the bar 105 shown in FIG. 7 andthe rod 106 shown in FIG. 10 . The bar 105 and the rod 106 may be madeof a variety of materials ranging from deformable plastics to hardmetals, depending upon the desired application. Thus, bars and rods ofthe invention may be made of materials including, but not limited tometal, metal alloys or other suitable materials, plastic polymers suchas polyetheretherketone (PEEK), ultra-high-molecular weight-polyethylene(UHMWP), polyurethanes and composites, including composites containingcarbon fiber, natural or synthetic elastomers such as polyisoprene(natural rubber), and synthetic polymers, copolymers, and thermoplasticelastomers, for example, polyurethane elastomers such aspolycarbonate-urethane elastomers. Whether the longitudinal connectingmember of the invention is a cord, rod or bar; hard-surfaced or soft anddeformable; or elastic or non-elastic, the combination of a limitedtravel closure top that allows the connecting member some movementwithin the bone screw further cooperating with a bumper and a connectorholding structure such as the crimping structure 10, advantageouslyallows for limited movement of the connector with respect to the bonescrew, creating a dynamic connection between spinal assembly andcooperating vertebrae.

With particular reference to FIGS. 8 and 9 , the bone screw 112 guideand advancement structure 118 that receives and mates with the limitedtravel closure 115 includes a run-out aperture or groove partiallydefined by a bottom or lower seating surface 117 sized and shaped forfrictional engagement with a portion of the closure 115. As shown inFIG. 9 , the closure 115 minor diameter is slightly bigger than therun-out groove so the closure 115 abuts against the surface 117 whendriven downward into the receiver. The seating surface 117 terminates atthe opposed planar surfaces 167.

The bone screw receiver 162 further includes opposed, substantiallyparallel outer side surfaces 170. It is foreseen that according to theinvention, other embodiments of the invention may include side surfacesthat angle away or towards one another for lordosing or kyphosingcontrolling embodiments as previously described in applicant'sapplication U.S. Ser. No. 11/328,481, the disclosure of which isincorporated by reference herein. It is also noted that the bone screw112 is identical or substantially similar to the bone screws describedin described in detail in Applicant's U.S. patent application Ser. No.12/584,980, the disclosure of which is incorporated by reference herein.

Specifically, the closure top 115 is substantially cylindrical andincludes a top surface 180, a bottom surface 182, a drive feature 184formed in the top surface 180 and an outer guide and advancementstructure 186 sized and shaped to mate with the guide and advancementstructure 118 of the bone screw 112. A cylindrical surface 188represents the minor diameter of a major portion of the closure 115. Theillustrated closure top 115 is rotatable between the spaced arms formingthe receiver 162 of the screw 112. The illustrated helically wound guideand advancement structure 186 is in the form of a flange form thatoperably joins with respective guide and advancement structure 118. Adriving tool or tools (not shown) sized and shaped for engagement withthe internal drive feature 184 is used for both rotatable engagementand, if needed, disengagement of the closure 115 from the screw 112. Theinternal drive feature 184 may take a variety of forms and may include,but is not limited to, a hex shape, TORX or other features or apertures,such as slotted, tri-wing, spanner, two or more apertures of variousshapes, and the like.

With particular reference to FIG. 9 , the closure top 115 is sized andshaped to cooperate with the run-out surface 117 to lock the closure 115on the bone screw 112 independent of any pressure being placed by theclosure 115 on the cord 104. Due to the size of the surface 188, thebottom surface 182 near the surface 188 forms a radially extending shelfor abutment seat. When the closure 115 is tightened by rotation into thescrew 112, the bottom 182 abuts against the surface 117, allowing theclosure to be tightened in the screw receiver 162 independent ofwhatever size cord 104 or other core, such as the bar 105 might be.Stated in another way, the closure 115 is prohibited from entering thespace between the planar surfaces 167 that support the cord 104 or othercore therebetween. Thus, it is not possible for the closure 115 to pressupon the cord 104, allowing such cord to slide between the closure top115 and the surfaces 167 and 168.

With reference to FIGS. 10-14 , a bone screw 112′ is illustrated that isidentical to the bone screw 112, having a receiver 162′, a shank 164′, arectangular channel 166′ formed by opposed planar surfaces 167′ and abottom surface 168′, the same or substantially similar to the receiver162, shank 164, channel 166, opposed planar surfaces 167 and bottomsurface 168 previously described herein with respect to the bone screw112. Further, the bone screw 112′ includes a lower seat 117′ of a guideand advancement structure 118′ and side surfaces 170′, the same orsimilar to the lower seat 117, guide and advancement structure 118 andside surfaces 170 of the bone screw 112. The bone screw 112 is shownwith the plastic, deformable rod 106 and a locking closure top 114having a lower extension portion 119 that is the same or similar to theclosure top 14 having the extended bottom portion 19 previouslydescribed herein with respect to the assembly 1.

The closure top 114 is substantially cylindrical and includes a topsurface 180′, a bottom surface 182′, a drive feature 184′ formed in thetop surface 180′ and an outer guide and advancement structure 186′ sizedand shaped to mate with the guide and advancement structure 118′ of thebone screw 112′. A cylindrical surface 188′ represents the minordiameter of a major portion of the closure 114. The illustrated closuretop 114 is rotatable between the spaced arms forming the receiver 162′of the screw 112′. The illustrated helically wound guide and advancementstructure 186′ is in the form of a flange form that operably joins withrespective guide and advancement structure 118′. A driving tool or tools(not shown) sized and shaped for engagement with the internal drivefeature 184′ is used for both rotatable engagement and, if needed,disengagement of the closure 115 from the screw 112. The internal drivefeature 184 may take a variety of forms and may include, but is notlimited to, a hex shape, TORX or other features or apertures, such asslotted, tri-wing, spanner, two or more apertures of various shapes, andthe like.

With particular reference to FIG. 14 , the closure top 114 is sized andshaped to cooperate with the run-out surface of the guide andadvancement structure 118′ to lock the closure 114 on the bone screw112′ independent of any pressure being placed by the closure 114 on thedeformable rod 106. In the illustrated embodiment, the closure 114includes a second cylindrical surface 190 located adjacent to and belowthe surface 188′ that defines the minor diameter of most of the closure114. The second cylindrical surface 190 has a second diameter smallerthan the minor diameter of the surface 188′. The outer surface 190partially defines the extended portion 119. The surface 190 is locatednear the bottom surface 182′ of the closure 114 that contacts andpresses against the deformable rod 106 or other longitudinal connectingmember core located within the bone screw receiver 162′ duringoperation. As shown in FIGS. 12 and 14 , the portion 119 presses againstand partially deforms the rod 106. A radially extending shelf orabutment seat 192 is formed between the cylindrical surface 188′ and thecylindrical surface 190. When the closure 114 is tightened by rotationinto the screw 112′, the seat 192 abuts against the surface 117′,allowing the closure to be tightened in the screw receiver 162′independent of the rod 106. The rod 106 is pressed upon and held inplace by the bottom surface 182′ of the screw, with some deformation ofthe rod 106 being acceptable and even desirable. In the illustratedembodiment, some of the rod material is allowed to flow up into an innerbore 195 of the closure 114. However, because of the cooperation betweenthe seat 192 and the screw surface 117′, the rod 106 is protectedagainst over-deformation or crushing that might lead to instability andfailure. Furthermore, if the rod 106 exhibits creep or other deformationduring operation, loosening or lessening of the contact engagementbetween the closure bottom surface 182′ and the rod 106 will not resultin loosening of the closure 114 from the screw 112′.

With reference to FIGS. 15 and 16 , an assembly 201′ according to theinvention is illustrated that provides for dynamic stabilization similarto the assembly 1 utilizing polyaxial bone screws. The illustratedassembly 201 includes a solid, hard-surfaced rod 204, a spacer 206, anelastic bumper 208, a crimping structure 210 and a pair of polyaxialbone screws 212A and 212B. The bone screws 212A and 212B are identicalor substantially similar to those described in Applicant's U.S. patentapplication Ser. No. 12/229,207, filed Aug. 20, 2008 entitled “PolyaxialBone Anchor Assembly With One-Piece Closure, Pressure Insert and PlasticElongate Member,” (hereafter, the '207 application), the disclosure ofwhich is incorporated by reference herein. A closure top 214 fixes therod 204 in the bone screw 212A and a closure top 215 captures the rod204 in the bone screw 212B, but a bottom surface 282 thereof does notfix the rod 204 with respect to the bone screw 212B as illustrated inFIG. 16 . (See, e.g., FIGS. 15-18 of the '207 application forillustrations of fixing of a rigid or deformable rod with a bone screwthe same or similar to the screw 212A). Each screw 212A and 212B furtherincludes a receiver 203 for slidingly pivotally receiving a bone screwshank upper portion, and a lower pressure insert 205 having surfaces forengaging the shank upper portion and surfaces for closely receiving therod 204. With reference to FIG. 16 , the closure top 215 lower surface282 engages upper arm surfaces 283 of the pressure insert 205 to capturethe rod 204 and lock the polyaxial mechanism of the bone screw 212B.Thus, the captured rod 204 is in sliding engagement with the screw 212B.The spacer 206, elastic bumper 208 and the crimping structure 210 arethe same or similar in form and function to the spacer 6, bumper 8 andcrimping structure 10 previously described herein with respect to theassembly 1, with the crimping structure 210 directly engaging the rod204. In alternative embodiments, a cord or deformable rod may beutilized in lieu of the illustrated rigid rod 204. The pressure insert205 may also be configured to receive a square or rectangular bar.

It is to be understood that while certain forms of the present inventionhave been illustrated and described herein, it is not to be limited tothe specific forms or arrangement of parts described and shown.

What is claimed is:
 1. A medical implant assembly comprising: a firstbone anchor having a first receiver; a second bone anchor having asecond receiver; a channel defined by the second receiver; a tensionablecord extending from a first end to a second end, the tensionable cordextending entirely through the channel and moveable relative to thesecond receiver; a rigid end structure having a substantiallycylindrical bore defined by first and second circular openings, anoutward end surface, and an opposed inward end surface, the tensionablecord extending through the first and second circular openings; a spacersurrounding the tensionable cord and located between the first receiverand the second receiver; and a bumper located between the rigid endstructure and the second receiver, engaging the inward end surface ofthe rigid end structure, and surrounding the tensionable cord, whereinthe tensionable cord is configured to be tensioned by a tool engagingthe outward end surface of the rigid end structure.
 2. The medicalimplant assembly of claim 1, wherein the spacer is compressible.
 3. Themedical implant assembly of claim 2, wherein the bumper is compressible.4. The medical implant assembly of claim 2, wherein the first circularopening is defined by a first diameter and the second circular openingis defined by a second diameter equal to the first diameter.
 5. Themedical implant assembly of claim 1, wherein the rigid end structure isconfigured to capture the tensionable cord under tension.
 6. The medicalimplant assembly of claim 5, wherein the rigid end structure isconfigured to be compressed against the bumper when the tensionable cordis tensioned and before the rigid end structure releasably captures thetensionable cord.
 7. The medical implant assembly of claim 1, whereinthe rigid end structure is configured to be compressively crimpedagainst the tensionable cord after the tensionable cord has beentensioned.
 8. The medical implant assembly of claim 1, wherein the firstbone anchor and the second bone anchor are polyaxial screws.
 9. Amedical implant assembly comprising: a first bone anchor; a second boneanchor; a tensionable cord connected to the first bone anchor at one endthereof, the tensionable cord extending entirely through the second boneanchor and in slidable relation with the second bone anchor; a rigid endstructure having a portion with a smooth non-threaded channel defined byfirst and second circular openings, an outward end surface, and anopposed inward end surface, the tensionable cord extending entirelythrough the channel, the rigid end structure configured to releasablycapture the tensionable cord under tension; a spacer surrounding thetensionable cord and located between the first bone anchor and thesecond bone anchor; and a bumper located between the rigid end structureand the second bone anchor, engaging the inward end surface of the rigidend structure, and surrounding the tensionable cord, wherein thetensionable cord is configured to be tensioned by a tool engaging theoutward end surface of the rigid end structure and the rigid endstructure is configured to be compressed against the bumper when thetensionable cord is tensioned before the rigid end structure releasablycaptures the tensionable cord.
 10. The medical implant assembly of claim9, wherein the rigid end structure is configured to be compressivelycrimped against the tensionable cord after the tensionable cord has beentensioned.
 11. The medical implant assembly of claim 9, wherein thefirst bone anchor and the second bone anchor are polyaxial screws. 12.The medical implant assembly of claim 9, wherein the first bone anchorand the second bone anchor each have a receiver with a top openingchannel.
 13. The medical implant assembly of claim 9, wherein the spacerand the bumper are compressible.
 14. The medical implant assembly ofclaim 9, wherein the channel is substantially cylindrical.
 15. Themedical implant assembly of claim 9, wherein the first circular openingis defined by a first diameter and the second circular opening isdefined by a second diameter equal to the first diameter.
 16. A methodof tensioning the tensionable cord in the medical implant assembly ofclaim 9, the method comprising: providing the medical implant assemblyof claim 9; engaging, with the tool, the outward end surface of therigid end structure; and tensioning, with the tool, the tensionablecord.
 17. A medical implant assembly comprising: a first bone anchorhaving a first receiver; a second bone anchor having a second receiver;a channel defined by the second receiver; a tensionable cord extendingfrom a first end to a second end, the tensionable cord extendingentirely through the channel and moveable relative to the secondreceiver; a rigid end structure having a substantially cylindrical boredefined by first and second circular openings, the tensionable cordextending through the first and second circular openings; a spacersurrounding the tensionable cord and located between the first receiverand the second receiver; and a bumper surrounding the tensionable cordand located between the rigid end structure and the second receiver,wherein the rigid end structure is configured to be compressivelycrimped against the tensionable cord after the tensionable cord has beentensioned.
 18. A method of tensioning the tensionable cord in themedical implant assembly of claim 17, the method comprising: providingthe medical implant assembly of claim 17; tensioning the tensionablecord; and compressively crimping the rigid end structure against thetensionable cord.
 19. The method of claim 18, wherein the rigid endstructure is configured to be compressively crimped against thetensionable cord after the tensionable cord has been tensioned.
 20. Amethod of tensioning the tensionable cord in the medical implantassembly of claim 1, the method comprising: providing the medicalimplant assembly of claim 1; engaging, with the tool, the outward endsurface of the rigid end structure; and tensioning, with the tool, thetensionable cord.